If your garage door faces south you can build a set of passive solar doors that will provide heat and light, reducing your energy expenses during winter for around $400 in materials.

Solar project resource site Build It Solar notes that plans for the solar enclosure do not block opening and closing your rolling garage door; they actually recommend lowering your door at night to help avoid avoid heat loss. You can also add a layer of thermal shades for additional heat retention. The additional doors are installed outside on the frame of your existing garage door.

The author's project was featured in Home Power magazine where he concluded that on a sunny winter day his shop was usually at 70 degrees Fahrenheit while the temperatures outside dropped to -20 degrees. If you actively use your garage as a shop and must heat it with a space heater you'll find that you'll recoup the costs of construction in energy savings in around two years, depending of course on local temperatures and utility costs.

It may seem strange to talk about a winter project now in the dog days of summer, but by the time you get the materials lined up and find the time to build you might be closer to using it than you would think. If you spend time in your garage instead of just parking your cars inside there are a lot of benefits with the major drawback of having to open both sets of doors to get your car inside.